Detailed studies have demonstrated that neural circuits in the central nervous system set the pattern for motor activity in many oscillatory behaviors. These endogenous pattern generator circuits are essential to behaviors in invertebrates (e.g. leech swimming) as well as in vertebrates (e.g. fish swimming) and probably control many human behaviors such as respiration and locomotion. The experiments described in this proposal are designed to uncover the neural mechanisms which control an endogenous pattern generation circuit in a model system, the cockroach flight system. This has been chosen for the following reasons: 1.) Normal flight activity can readily be elicited in highly dissected and restrained animals. 2.) Neurons that initiate activity in the pattern generation circuit are large and can be identified as individuals from animal to animal. 3.) Considerable control of patterned activity can be exerted by stimulating particular leg nerves. 4.) Work on similar preparations indicates a reasonable chance of success in uncovering the cellular components of the pattern generation circuit. Our specific aims are to 1.) describe the neural organization of the pattern generation circuit, 2.) determine how an unpatterned signal in giant interneurons of the abdominal nerve cord initiates patterned flight activity, 3.) determine how activation of sensory receptors on legs prevents or terminates patterned flight activity and 4.) determine how auxiliary neurons, not primarily involved in flight posture in the animal's entire body. All of these goals will be pursued in detail, using intracellular recording and stimulation techniques. These allow us to study each cellular component of the system as an individual either by itself or paired with other individual components. Our hope is to uncover principles which are generalizable to other systems. In so doing we would shed light on the control of oscillatory activities that are crucial to human physiology and behavior, and thereby contribute to our ability to deal with disorders of these systems.